Is Unlimited Data Making a Carrier Comeback?

For a while, unlimited data plans at wireless carriers were headed the way of the dodo. The two largest carriers, AT&T (NYS: T) and Verizon (NYS: VZ) , have been choking them to death over the past couple of years.

Ma Bell axed them back in 2010, although some users are still grandfathered in, while Big Red followed suit in 2011. Just this year, Verizon also went the extra step and killed the option for existing grandfathered subscribers as it not-so-gently pushes everyone toward its pricey Share Everything plans, which include a shared data bucket and unlimited voice and text.

Smaller rival Sprint Nextel (NYS: S) has taken the opportunity to pitch its unlimited data plans as a point of competitive advantage, as one of the remaining holdouts still offering an all-you-can-eat data buffet to users as it works to catch up on its 4G LTE network rollout, transitioning away from WiMAX.

T-Mobile has also kept "unlimited" data plans alive, but with a catch that after a certain threshold the carrier begins to throttle, or limit, data speeds to unbearable levels. Well, the company has just announced that it will begin offering an unlimited data plan with no throttling next month.

The key thing to point out is that both Sprint and T-Mobile, the two current proponents among the four largest carriers, are far behind in their 4G LTE networks, so the real question is whether or not subscribers would rather have limited 4G LTE or unlimited 3G/4G HSPA+. Seems like the sweet spot of unlimited 4G LTE is just out of reach, unless...

Enter MetroPCS (NYS: PCS) , which just announced that it's offering an unlimited 4G LTE data plan, although this is a promotional deal only available for a limited time. Of course, the catch here is that MetroPCS' LTE coverage is also rather limited, so again there's a trade-off for customers.

At least there's an indication that carriers aren't giving up entirely on unlimited data, or that it can at least be perceived as a value proposition from the smaller players while the two top dogs hope to use other advantages in size instead. Unlimited data ain't dead quite yet.